Expansion anchor with grooves in the expansion cone

ABSTRACT

An expansion anchor with a bolt and at least one expansion element is disclosed. An oblique surface is arranged in the region of the first end of the bolt and forces the expansion element radially outward on the bolt if the bolt is displaced in a pull-out direction relative to the expansion element. The bolt has, in the region of its rear end facing away from the first end, a load-absorber which is suitable for introducing tensile forces which are directed in the pull-out direction into the bolt. At least one groove which is closed with respect to the first end is made in the oblique surface, which groove reduces the contact surface between the expansion element and the oblique surface.

This application claims the priority of International Application No.PCT/EP2014/073630, filed Nov. 4, 2014, and European Patent Document No.13191706.4, filed Nov. 6, 2013, the disclosures of which are expresslyincorporated by reference herein.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to an expansion anchor. Such an expansion anchoris equipped with a bolt and an expansion element, and an oblique surfaceis arranged in the region of the first end of the bolt which forces theexpansion element radially outwards if the bolt is displaced in apull-out direction relative to the expansion element, and the bolt has,in the region of its rear end facing away from the first end, aload-absorbing means which is suitable for introducing tensile forceswhich are directed in the pull-out direction into the bolt.

A generic expansion anchor is, for example known from U.S. Pat. No.5,176,481 A. This expansion anchor can be used to anchor components to abore hole in a solid substrate, for example in concrete. The knownexpansion anchor has an elongated bolt. The bolt has a cone-shapedexpansion section in the region of its first rear end, the expansionsection expands towards the first end i.e., against the pull-outdirection. An expansion sleeve mounted displaceable towards the firstend on the expansion section is arranged in the pull-out direction nextto the expansion section. The expansion sleeve has elevations on theouter side which protrude in a radial direction over the bolt and bymeans of which the expansion sleeve can lock onto the inner wall of thebore hole in the substrate. The expansion anchor is inserted into thebore hole against the pull-out direction with the first end forwards andthe bolt is subsequently pulled back out of the bore hole in thepull-out direction to a certain extent. After inserting the expansionanchor, the expansion sleeve is locked onto the inner wall of the borehole and is thus retained in the bore hole when the bolt is pulled out.The expansion section of the bolt is hereby pulled into the expansionsleeve, and the expansion sleeve is spread apart due to the increasingdiameter of the expansion section and the expansion anchor locks withthe expansion sleeve in the substrate so that loads can be transferredinto the substrate. This basic principle can also be expedientlyimplemented in the invention.

U.S. Pat. No. 5,176,481 A also teaches to provide the bolt with afriction-reducing coating in the region of the expansion sleeve.

Further expansion anchors are known from DE 2256822 A1, and DE 2256822A1 teaches positive anti-twist protection between the expansion sleeveand bolt. According to DE 2256822 A1, for example, a notch can beprovided on the bolt which extends, to a certain extent, into theexpansion cone from the neck of the bolt, and a corresponding projectionis arranged on the expansion sleeve which follows the notch in thecross-section of the anchor and engages into the notch.

US2011081217 AA and DE102011076180 A1 describe expansion anchors in thecase of which the expansion cone has a non-circular cross-section with aplurality of maximum heights and a plurality of minimum heights.

The object of the invention is to indicate a particularly efficient andversatilely usable expansion anchor that is at the same time alsoparticularly reliable and easy to manufacture.

An expansion anchor according to the invention is characterized in thatat least one, preferably elongated groove that is closed with respect tothe first end of the bolt is made in the oblique surface, the groovereduces the contact surface between the expansion element and theoblique surface.

The invention is based on the knowledge that when expansion anchors aredesigned, the situation may arise whereby a change to the design of theanchor at one point leads to an improvement of the anchor behavior, butthis is, however, associated with losses at other points. It may thus,for example, on the one hand be desirable to provide a high frictioncoefficient between the oblique surface and the expansion element inorder to avoid the oblique surface pulling through the expansionelement, i.e., in particular through the expansion sleeve and thuspremature failure of the anchor in the case of excessive static tensileloads. On the other hand, a high friction coefficient between theoblique surface and expansion element may increase the probability ofthe anchor not taking hold at the beginning of the setting process andis pulled out of the bore hole in an undesired manner. Furthermore, anexcessively high friction coefficient between the oblique surface andexpansion element may be disadvantageous with regard to the dynamicproperties in fractured concrete. If namely the friction coefficientbetween the oblique surface and expansion element is large, then thebolt is drawn deep into the expansion sleeve if a fracture opens in theregion of the anchor. However, this process is not reversed for a largefriction coefficient if the fracture is subsequently closed again andthe oblique surface remains deep in the expansion sleeve which may leadto damage of the surrounding concrete. A low friction coefficient maythus be advantageous for fractured concrete in order to ensure“pumping”, i.e., sliding the oblique surface forwards and backwards inthe expansion sleeve in the case of a fracture opening and subsequentfracture closure.

In the design of a conventional anchor, a decision must thus be made asto whether a low friction coefficient between expansion element and theoblique surface is selected with regard to good properties in fracturedconcrete with movable fractures, which is, however, associated with alower static tensile load, or whether a high friction coefficient isselected, which leads to high static tensile loads, but to inferiorproperties in fractured concrete.

The invention begins here and provides at least one groove in theexpansion region of the bolt in the oblique surface, i.e., in particulara depression which extends radially into the bolt interior from the boltsurface. This groove reduces the frictional contact surface between theexpansion element and the oblique surface, i.e., due to the groove, thecontact surface between the expansion element and the oblique surface issmaller than if the groove were absent and the oblique surface wereadvanced there instead of corresponding to the opposing inner surface ofthe expansion element. The groove can thus reduce the friction inprecisely that region of the expansion cone where the expansion elementin fractured concrete rubs so that the previously described “pumping” ismade easier in the case of a fracture opening and subsequent fractureclosure and damage to the concrete is effectively prevented. Accordingto a further basic concept of the invention, the groove is, in thisrespect, closed with respect to the anchor tip. In particular, thegroove is thus covered and not visible when viewed from in front of theanchor with a viewing direction parallel to the longitudinal axis of thebolt. According to the invention, a groove-free region is herebyprovided in front of the groove, preferably between the bolt tip andexpansion cone. If the expansion element reaches into this groove-freeregion in the case of large static loads, then the friction of theexpansion element can increase disproportionately such that a prematurepulling of the bolt through the expansion element is avoided. Thepreviously described contradiction between good properties in fracturedconcrete and high static tensile loads in unfractured concrete can thusbe solved by the groove according to the invention. As a result, aparticularly reliable and versatilely usable anchor can be madeavailable in a particularly simple manner. In particular, a costly,friction-reducing coating can often even be dispensed with. In certainload and application areas however, such a coating may also be provided;the invention does not exclude this.

The groove can end at its side facing the anchor tip, i.e., at its sidefacing away from the rear end of the bolt, already inside the obliquesurface or only further forward on the bolt. The local friction-reducingeffect of the groove can be based on the reduction of the contactsurface between oblique surface and expansion element and/or on othermechanisms such as the inclusion and concentration of bore dust.

According to the invention, the expansion element is arranged, inparticular fastened on the bolt displaceable along on the bolt. Insofaras “radial”, “axial” and “circumferential direction” are mentioned here,this may, in particular, relate to the longitudinal axis of the boltwhich may, in particular, be the symmetry and/or center axis of thebolt. The expansion anchor can preferably be a force-controlledexpanding expansion anchor. The expansion element and/or the boltsuitably consist of a metal material which, as already mentioned, canalso be coated for further selective influence of the friction. Theload-absorbing means can, in particular, be designed as an outer threador as an inner thread. It serves for introducing tensile forces into thebolt which are directed in the pull-out direction. The bolt can also bepartially hollow.

According to the invention, the expansion element is forced radiallyoutwards from the oblique surface and, in this respect, pressed againstthe bore hole wall in the substrate if the oblique surface, inparticular together with the bolt, of the bolt is axially displaced inthe pull-out direction relative to the expansion element. The expansionanchor is hereby anchored in the bore hole. Preferably, the pull-outdirection runs parallel to the longitudinal axis of the bolt and/orpoints outside the bore hole. In particular, the direction vector of thepull-out direction can be directed from the oblique surface to theload-absorbing means. At the oblique surface, the distance of the boltsurface from the longitudinal axis of the bolt increases contrary to thepull-out direction, i.e., with increasing distance from theload-absorbing means.

It is particularly preferred for the expansion element to be anexpansion sleeve which surrounds the bolt at least in regions and/or forthe bolt to have an expansion cone, and the oblique surface is formed bythe expansion cone. A particularly balanced introduction of force in thecircumferential direction is hereby achieved. According to theinvention, the expansion cone is provided for spreading apart theexpansion sleeve, i.e., for radially expanding the expansion sleeve. Anexpansion element or even a plurality of expansion elements can beprovided and a corresponding number of oblique surfaces. The expansionsleeve can have expansion slots which start from the front face of theexpansion sleeve. These expansion slots can facilitate the radialexpansion of the expansion sleeve by the expansion cone of the bolt.

In the case of a so-called bolt anchor, the expansion cone can bearranged axially fixed to the bolt. In this case, the expansion cone isdrawn with the oblique surface into the expansion sleeve when theexpansion anchor is set by a common axial movement of the bolt and theexpansion cone relative to the expansion sleeve. The expansion cone is,in this respect, preferably designed integrally with the bolt.Alternatively, in the case of a so-called sleeve anchor, the expansioncone can be a part that is separate from the bolt and is preferablyconnected via corresponding threads with the bolt. The drawing of theexpansion cone into the expansion sleeve can then preferably be producedat least partially by rotation of the bolt relative to the expansioncone which is implemented by a spindle drive, formed by thecorresponding threads, into an axial movement of the expansion conerelative to the bolt.

It is particularly expedient for the bolt to have a tip region whichattaches to the expansion cone on the side of the expansion cone facingthe first end and in which the cross-section of the bolt is at least aslarge as in the expansion cone, and the groove ends before the tipregion or in the tip region. According to this embodiment, in whichbefore the tip region another relatively large cross-sectional tipregion is arranged, into which, in any case, the at least one groovepartially extends, a particularly suitable force path may be obtained,which, in particular, effectively counteracts the bolt pulling throughthe expansion sleeve particularly.

It is particularly preferred for the expansion of the groove in theaxial direction of the bolt to be greater than the expansion of thegroove in the circumferential direction of the bolt. In particular, thegroove can, preferably over its entire length, run on the obliquesurface along a projection of the longitudinal axis of the bolt. Thegroove can, in addition or alternatively, run parallel to thelongitudinal axis of the bolt, i.e., in the axis longitudinal directionand/or axial direction. Tilting between the expansion element and boltcan be hereby simply and effectively counteracted.

It is particularly expedient for the inner surface of the expansionelement to be smooth in the region of the groove and/or the expansionelement to not engage into the groove, in each case at least in theunset starting state of the anchor. In particular, the expansion elementadvantageously does not have a projection engaging into the groove onits inner side facing the oblique surface and in particular the bolt. Aparticularly reliable, local friction reduction may be hereby achieved.For the same reason, the region of the inner cross-section of theexpansion element which comes to rest against the groove in the setstate of the anchor is preferably concave. For example, the innersurface of the expansion element can be designed in a cylindricallyconcave manner in this region. In particular, the expansion element, atleast in the unset starting state of the anchor, is distanced at thegroove from the surface of the oblique surface. The expansion element,at least in the starting state of the anchor, thus does not reach intothe groove at least not to the base of the groove. The cross-section ofthe expansion cone in the surface regions of the expansion cone, whichrun displaced with respect to the groove viewed in the circumferentialdirection, expediently corresponds to the cross-section of the opposinginner side of the expansion element, whereas the cross-section of theexpansion cone at the groove deviates from the cross-section of theopposing inner side of the expansion element. Insofar as a plurality ofgrooves are provided, the cross-section of the expansion cone betweenthe grooves expediently corresponds to the cross-section of the opposinginner side of the expansion element, whereas the cross-section of theexpansion cone at the grooves deviates from the cross-section of theopposing inner side of the expansion element.

Moreover, it is advantageous for a plurality of grooves closed withrespect to the first end of the bolt to be made into the obliquesurface, which respectively reduce the contact surface between theexpansion element and the oblique surface. The friction can even behereby further reduced and the previously described “pumping” supportedeven better. The grooves are preferably all the same length. Theypreferably all begin at the same axial position and/or preferably allend at the same axial position. Insofar as a plurality of groovesaccording to the invention are provided, the features described in thisdocument can apply for one of these grooves, for a part of the groovesor for all grooves. It is particularly preferred for at least fourgrooves closed with respect to the first end of the bolt to be made intothe oblique surface, in particular at least one groove percross-sectional quadrant of the bolt, with regard to its longitudinalaxis, which may then in particular be advantageous if the expansionelement is an expansion sleeve and the oblique surface is formed by anexpansion cone. The bolt preferably has a circular segment-shapedcross-section between adjacent grooves.

In particular for a particularly balanced force path and thus high loadsand high reliability, provision can also be made for the grooves, inparticular in the cross-section perpendicular to the longitudinal axisof the bolt, to be arranged equidistant and/or for the grooves to bedistributed evenly around the expansion cone. The last-mentioned featurecan then be advantageous in particular if the expansion element is anexpansion sleeve. Equidistant arrangement can, in particular, beunderstood as adjacent grooves always having the same angular distanceat the bolt longitudinal axis in the cross-section of the anchorperpendicular to the bolt longitudinal axis.

The grooves are particularly effective if the contact surface betweenthe expansion element and the oblique surface is reduced by the groovesby 20 to 50%.

The individual grooves are expediently relatively narrow, for example inorder to avoid the expansion element being bent into the grooves when itis spread apart. Accordingly, it is particularly preferred for themaximum angular width of the at least one groove measured in thecross-section of the bolt at the longitudinal axis to be smaller than30°, in particular smaller than 15°.

The invention can, in particular, be used in bolt anchors in which theexpansion sleeve does not reach to the bore hole mouth in the case ofthe set anchor. Because in the case of bolt anchors, the expansionprocess is particularly strongly influenced by the individual frictionalprocesses at the anchor. Accordingly, a stop can be designed on the boltwhich limits a displacement of the expansion element away from theoblique surface, in particular a displacement in the pull-out direction.Such a stop can, in the case of a bolt anchor, particularly simplyensure that the expansion element, together with the bolt, reliablypenetrates into the bore hole. The stop is preferably an annularshoulder which may be advantageous in terms of manufacturing and inrelation to reliability. In particular, the stop is axially arrangedbetween the oblique surface and the load-absorbing means.

The invention is explained in greater detail below by means of preferredexemplary embodiments, which are schematically depicted in the enclosedfigures, and individual features of the exemplary embodiments shownbelow can be implemented in the context of the invention essentiallyindividually or in any combination.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial longitudinal section view of an expansion anchoraccording to the invention set in a concrete substrate; and

FIG. 2 is a perspective view of the bolt of the anchor from FIG. 1 inthe region of the front, first end of the bolt.

DETAILED DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 3 show an exemplary embodiment of an expansion anchor 1according to the invention. As in particular FIG. 1 shows, the expansionanchor 1 has a bolt 10 and an expansion element 20 designed as anexpansion sleeve, and the expansion sleeve surrounds the bolt 10 in acircular manner. The bolt 10 has a neck region 11 in the region of itsfront end 51, an expansion cone 12 for the expansion sleeve 20continuously attached on the front side to the neck region 11 and a tipregion 14 continuously attached to the expansion cone 12 on the frontside.

The bolt 10 has a substantially constant cylindrical cross-section inthe neck region 11. On the expansion cone 12 attached thereto, thesurface of the bolt 10 is designed as an oblique surface 13 and thediameter of the bolt 10 increases there towards the first end 51, i.e.,the bolt 10 expands at the expansion cone 12 starting from the neckregion 11 towards its front first end 51 and towards the tip region 14.The oblique surface 13 on the expansion cone 12 can be conical in thestrictly mathematical sense, however it does not have to be. In the tipregion 14, the bolt cross-section is ultimately substantially constantor increases at least towards the first end 51 less strongly than at theexpansion cone 12.

The bolt 10 has a stop 17 for the expansion sleeve 20 designed, forexample as an annular shoulder on the side of the neck region 11 facingaway from the expansion cone 12. The bolt has a load-absorbing means 18in the region of its rear end 52 for introducing tensile forces into thebolt 10, which is designed here by way of example as an outer thread. Anut 8 sits on this outer thread.

When the expansion anchor 1 is set, the bolt 10 is inserted into a borehole 99 in the substrate 5 from FIG. 1 with its first end 51 forwards inthe direction of the longitudinal axis 100 of the bolt 10. Due to thestop 17, which limits a displacement of the expansion element 20 awayfrom the expansion cone 12, the expansion element 20 designed as anexpansion sleeve is also, in this respect, introduced into the bore hole99. The bolt 10 is then, for example by tightening the nut 8, pulledback out from the bore hole 99, to a certain extent, in the pull-outdirection 101 running parallel to the longitudinal axis 100. Due to itsfriction on the substantially cylindrical wall 98 of the bore hole 99,the expansion element 20 designed as an expansion sleeve remains, inthis respect, in the bore hole 99 and as a result there is adisplacement of the bolt 10 relative to the expansion element 20. In thecase of this displacement, the oblique surface 13 of the expansion cone12 of the bolt 10 penetrates increasingly deeper into the expansionelement 20 such that the expansion element 20 is radially expanded fromthe oblique surface 13 and is pressed in with the wall 98 of the borehole 99. The expansion anchor 1 is fixed in the substrate 5 by way ofthis mechanism. The set state of the expansion anchor 1, in which it isfixed in the substrate 5, is shown in FIG. 1. An attachment part 6 canbe fixed on the substrate 5 by means of this nut 6.

A plurality of grooves 80 are provided in the expansion cone 12 whichare evenly distributed, thus with constant surface density, on theexpansion cone 12. The grooves 80 extend respectively in the directionof the respectively largest gradient of the expansion cone 12,respectively parallel to a projection of the longitudinal axis 100 onthe surface of the expansion cone 12. The grooves 80 all have the sameaxial length and end at their one side at the transition of the neckregion 11 into the expansion cone 12 and at their other side prior toreaching the tip region 14. The grooves 80 locally reduce the frictionbetween the expansion element 20 and the bolt 10 such that in fracturedconcrete a low friction coefficient is provided which allows the bolt 10to be slid forwards and backwards in the expansion element 20 in thecase of a fracture opening and subsequent fracture closure. Since thegrooves 80 do not extend or only slightly extend into the tip region 14,the maximum friction between the expansion element 20 and bolt 10 andthus the maximum static pull-out load can, in this respect however,remain high.

The invention claimed is:
 1. An expansion anchor, comprising: a bolt;and an expansion element; wherein an oblique surface is disposed in aregion of a first end of the bolt, wherein the expansion element isforced radially outwards when the bolt is displaced in a pull-outdirection relative to the expansion element; wherein the bolt has, in aregion of a rear end of the bolt which faces away from the first end ofthe bolt, a load-absorber, wherein tensile forces which are directed inthe pull-out direction are introducible into the bolt by theload-absorber; and wherein a groove that is closed with respect to thefirst end of the bolt, such that the groove is covered and not visiblewhen viewed from in front of the expansion anchor with a viewingdirection along a longitudinal axis of the bolt, is disposed in theoblique surface and wherein the groove reduces a contact surface betweenthe expansion element and the oblique surface.
 2. The expansion anchoraccording to claim 1, wherein the expansion element is an expansionsleeve which surrounds the bolt at least in regions and wherein theoblique surface is formed by an expansion cone.
 3. The expansion anchoraccording to claim 2, wherein the bolt has a tip region which attachesto the expansion cone on a side of the expansion cone that faces thefirst end of the bolt, wherein in the tip region a cross-section of thebolt is at least as large as a cross-section of the bolt in theexpansion cone, and wherein the groove ends before the tip region or inthe tip region.
 4. The expansion anchor according to claim 1, wherein anexpansion of the groove in an axial direction of the bolt is greaterthan an expansion of the groove in a circumferential direction of thebolt and wherein the groove runs along a projection of the longitudinalaxis of the bolt on the oblique surface.
 5. The expansion anchoraccording to claim 1, wherein an inner surface of the expansion elementis smooth in a region of the groove and/or the expansion element doesnot engage into the groove.
 6. The expansion anchor according to claim1, wherein a plurality of grooves that are closed with respect to thefirst end of the bolt are disposed in the oblique surface and whereinthe plurality of grooves reduce the contact surface between theexpansion element and the oblique surface.
 7. The expansion anchoraccording to claim 6, wherein the plurality of grooves are disposedequidistant.
 8. The expansion anchor according to claim 6, wherein thecontact surface between the expansion element and the oblique surface isreduced by the plurality of grooves by 20 to 50%.
 9. The expansionanchor according to claim 1, wherein a maximum angular width of thegroove measured in a cross-section of the bolt at the longitudinal axisis smaller than 30°.
 10. The expansion anchor according to claim 1,wherein the bolt has a stop and wherein the stop limits a displacementof the expansion element away from the oblique surface.
 11. Theexpansion anchor according to claim 10, wherein the stop is an annularshoulder.